1. Field of the Invention
The present invention relates to a method of manufacturing a cathode for a plasma etching apparatus, and a cathode manufactured thereby. More particularly, the present invention relates to a method of manufacturing a cathode which includes a chemical surface treatment of the silicon substrate from which the cathode is manufactured, in which the protrusions formed inside the holes and on the surface of the silicon substrate are removed using potassium hydroxide (KOH).
2. Background of the Related Art
In general, semiconductor devices are manufactured by forming layers on a semiconductor wafer, and forming a specific pattern on the layers according to the desired characteristics of the semiconductor devices. The specific pattern can be formed by completely or selectively removing certain layers on the wafer using an etching process.
The wet etching process, which was widely used to accomplish the layer removal, has been replaced by a dry etching process using plasma to produce highly-integrated semiconductor devices. Referring to FIG. 1, a conventional etching chamber for carrying out a dry etching process using plasma comprises a cathode 10 serving as an upper electrode to which a high frequency power is applied, and a chuck 14 (normally an electrostatic chuck) located beneath the cathode 10 for mounting a wafer 12. Beneath the chuck 14, there is provided an anode 16 serving as a lower electrode, and a power applier 18 for applying a high frequency power to the cathode 10 and the anode 16.
A plurality of holes for supplying gas into the etching chamber during the etching process are formed in the cathode 10, and a gas supplier 20 is provided for supplying the gas into the etching chamber. In addition, a baffle 22 is provided on top of the cathode 10, such that the gas is uniformly supplied to the entire surface of the wafer 12.
The etching chamber also includes: an RF matching box 24 for matching the condition of high frequency power applied to the etching chamber; a remote power module 26 for controlling process conditions related to the etching chamber; a temperature control unit 28 for controlling the temperature of the etching chamber; and a chuck power unit 32 for supplying power to a pump 30 and the chuck 14.
The cathode 10 of the etching apparatus can be made using aluminum, with a surface of anodized aluminum, quartz, ceramic, etc. Furthermore, to improve the uniformity of a layer to be etched during the etching process, the cathode 10 can be made of a silicon substrate, the same material as the wafer 12.
However, a cathode made of silicon substrate also serves as source of particles, just as cathodes made of aluminum, aluminum with an anodized surface, quartz, ceramic, etc., serve as sources of particles. The particles are generated from protrusions existing on the surface of the cathode 10 and inside the holes formed in the cathode 10. FIG. 2 shows the surface of the cathode 10 magnified 800 times using a microscope, and FIG. 3 shows the inside of the holes formed in the cathode 10 magnified 4,000 times using a scanning electron microscope.
These protrusions in the cathode 10 as shown in FIGS. 2 and 3 create particles, because the protrusions are etched off of the cathode 10 while a layer of the wafer 10 is being etched.
In other words, plasma formed inside the etching chamber reacts with the surface of the cathode 10 made of silicon substrate, such that the protrusions present on the surface of the cathode 10 are etched and separated as particles, and these particles attach to the wafer located beneath the cathode 10.
The plasma enters the holes in the cathode 10, and then reacts with the inside of the holes so that the protrusions inside the holes are also etched and separated, and then attach to the wafer.
The protrusions etched and separated from the inside and surface of the holes on the cathode 10 quickly adhere to the wafer due to the electrostatic force of the chuck 14 on which the wafer 12 is mounted.
While the etching process using the conventional cathode 10 made of silicon substrate is continuously carried out, the protrusions on the inside and on the surface of the holes in the cathode 10 are continuously etched and separated. Eventually, a slippery, hard surface is formed on the cathode 10 such that no further etching and separation is possible, as illustrated in FIG. 4 showing the inside of the holes formed on the cathode 10 magnified 800 times.
Then, the etching process can be carried out for a certain time with the inside and the surface of the holes of the cathode 10 formed as a hard surface.
However, even if particles are no longer generated from the hard surface of the cathode 10, the diameter of the holes has been enlarged by the etching and separation of the protrusions in the inlet of the holes, and the etching conditions have been changed. For example, the amount of gas supplied during the etching process is changed due to the enlargement of the hole diameter.
The changes in the etching conditions cause distortion of the critical dimension of the wafer pattern. Accordingly, after carrying out the etching process for a certain time, the cathode 10 must be replaced. That is, the enlargement of the holes during the etching process, and the replacement of the cathode 10, result in reduction of the useful life of the cathode.
Furthermore, the conventional cathode 10 is a source of particles which cause failure of the etching process, thereby deteriorating the reliability of the process.